Novak Djokovic survived his first serious test of the ATP Tour Finals as the world number one advanced to the final with a 6-1, 3-6, 6-0 victory over Japan's Kei Nishikori on Saturday.

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Djokovic had swept through the group stage at London's O2 Arena in imperious style, but he was pushed harder by Nishikori, who became the first player to take a set off him this week, before a strong finish secured the Serb's fourth appearance in the final of the prestigious season-ending event.

The 27-year-old has now won 31 successive indoor matches, including 14 at the Tour Finals, and his final opponent will be either six-time champion Roger Federer or Stan Wawrinka, who meet in an all-Swiss semi-final later on Saturday.